It is known that correction of certain optical defects can be accomplished by imparting non-spherical corrective characteristics to one or more surfaces of a contact lens such as cylindrical, bifocal, multifocal, and wavefront corrective characteristics. Additionally, lenses with non-rotationally symmetric tinted patterns, back surfaces that match corneal topography, and lenses with off-set optic zones are known. The use of these lenses is problematic in that the lenses must be maintained at a specific orientation while on the eye to be effective. When such a lens is first placed on the eye, it must automatically position, or auto-position, itself and then maintain that position over time. However, once the lens is positioned, it tends to rotate on the eye due to the forces exerted on the lens by the eyelids during blinking.
Maintenance of the on-eye orientation of a lens typically is accomplished by altering the mechanical characteristics of the lens. For example, prism stabilization, including, without limitation, decentering of the lens' front surface relative to the back surface, thickening of the inferior lens periphery, forming depressions or elevations on the lens' surface, and truncating the lens edge, has been used.
Additionally, dynamic stabilization has been used in which the lens is stabilized by the use of thick and thin zones, or areas in which the thickness of the lens' periphery is increased or reduced, as the case may be. Typically, the thin and thick zones are located symmetrically about the lens' periphery. For example, each of two thick zones may be positioned on either side of the optic zone and centered along the 0-180 degree axis of the lens. The symmetric stabilization zones are disadvantageous because one eyelid, the upper eyelid, for example, will strike one end of a stabilization zone before it strikes the other stabilization zone. This results in tilting of the lens moving it away from the orientation that is sought to be maintained.